[PATCH 1/2] ARM: KVM: Yield CPU when vcpu executes a WFE

Marc Zyngier marc.zyngier at arm.com
Tue Oct 8 11:06:59 EDT 2013

On 08/10/13 16:02, Raghavendra K T wrote:
> [...]
>>>> +               kvm_vcpu_on_spin(vcpu);
>>> Could you also enable CONFIG_HAVE_KVM_CPU_RELAX_INTERCEPT for arm and
>>> check if ple handler logic helps further?
>>> we would ideally get one more optimization folded into ple handler if
>>> you enable that.
>> Just gave it a go, and the results are slightly (but consistently)
>> worse. Over 10 runs:
>> Without RELAX_INTERCEPT: Average run 3.3623s
>> With RELAX_INTERCEPT: Average run 3.4226s
>> Not massive, but still noticeable. Any clue?
> Is it  a 4x overcommit? Probably we would have hit the code
> overhead if it were small guests.

Only 2x overcommit (dual core host, quad vcpu guests).

> RELAX_INTERCEPT is worth enabling for large guests with
> overcommits.

I'll try something more aggressive as soon as I get the time. What do
you call a large guest? So far, the hard limit on ARM is 8 vcpus.

Jazz is not dead. It just smells funny...

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